Abstract:The two nostrils inspire air from distinct regions in space, which provides an olfactory spatial gradient that contributes to odor localization. Such nostril-specific information is generally considered inaccessible by awareness. Whether it can be accessed by attention is hardly known. We show behaviorally that attention to an odor cue facilitates the detection of a subsequent odor target presented in the same, rather than the opposite, nostril. However, semantic instruction to direct attention to one nostril fails to produce a nostril-specific attentional gain. Corroborating the behavioral results, preliminary fMRI data suggest that attention paid to an odor presented in one nostril, but not overtly to a specific nostril, augments activity in the ipsilateral piriform, despite that the participants are unaware of which nostril that odor is presented in. Our results suggest an overlap between object representation and spatial mapping in the olfactory system outside the scope of goal-directed spatial attention. They also demonstrate a dissociation between attention and awareness in olfaction.